Method and apparatus for detecting land pre-pits

ABSTRACT

Aspects of the disclosure provide a method for detecting land pre-pits. The method includes extracting a land pre-pit data stream from a signal responsive to land pre-pits on an optical medium based on a land pre-pit threshold, detecting a bit stream pattern from the land pre-pit data stream, comparing one or more bits in the land pre-pit data stream at locations relative to the bit stream pattern with pre-known bit information, and adjusting the land pre-pit threshold based on the comparison.

INCORPORATION BY REFERENCE

This application is a continuation of U.S. patent application Ser. No.12/249,248, “Method and Apparatus for Detecting Land Pre-Pits” filedOct. 10, 2008, which claims the benefit of U.S. Provisional ApplicationNo. 60/980,000, “Land Pre-Pit Detector with Adaptive Threshold” filed onOct. 15, 2007. The entire disclosures of the above-identifiedapplications are incorporated herein by reference in their entirety.

BACKGROUND

Land pre-pits can be used to embed information, such as addressinformation, disk information, for memory media, such as DVD-R, DVD-RAM,DVD-RW, and the like. For example, a memory medium may include a spiralgroove with a spiral land. The spiral groove and the spiral land can bewobbled to incorporate timing information. Additionally, a memorymedium, such as DVD-R, DVD-RAM and DVD-RW, may utilize land pre-pits,which can be in the form of little pieces of mirrors deposited atspecific locations of the spiral land of the memory medium, to embedaddress information and disk information. The land pre-pits can bedetected by a medium recording device to obtain the address informationand the disk information of the memory medium. The address informationand the disk information can assist the medium recording device torecord user data at the specific address in the spiral groove of thememory medium.

SUMMARY

However, land pre-pits can be incorrectly detected by a medium recordingdevice due to reasons, such as variations in manufacturing, noises andinterferences of adjacent grooves, and the like. Aspects of thedisclosure can provide a method for detecting land pre-pits. The methodcan adaptively adjust a threshold for detecting the land pre-pits inorder to improve the correctness of detecting.

The method for detecting land pre-pits can include extracting a landpre-pit data stream from a reading signal based on a land pre-pitthreshold, the reading signal corresponding to land pre-pits of anoptical medium, comparing the land pre-pit data stream with formatinformation of the optical medium to obtain an error signal, andadjusting the land pre-pit threshold based on the error signal.

Further, the method can include determining an initial land pre-pitthreshold during a calibration process.

To compare the land pre-pit data stream with the format information, themethod can further include detecting a SYNC frame from the land pre-pitdata stream, and comparing the land pre-pit data stream and the formatinformation with reference to the SYNC frame.

To extract the land pre-pit data stream, the method can further includecomparing the reading signal with the land pre-pit threshold todetermine a state, such as a binary state, of the reading signal.

Additionally, to adjust the land-pit threshold based on the errorsignal, the method can further include adjusting the land pre-pitthreshold based on an average of the error signal. Further, the methodcan include averaging the error signal based on a programmable gain.

To average the error signal based on the programmable gain, the methodcan further include multiplying the error signal with the programmablegain, and accumulating the multiplied error signal.

To adjust the land pre-pit threshold, the method can further includeadjusting a digital representation corresponding to the land pre-pitthreshold based on the error signal, and converting the digitalrepresentation to an analog voltage of the land pre-pit threshold.

According to an aspect of the disclosure, the optical medium is at leastone of DVD-R, DVD-RAM and DVD-RW.

Aspects of the disclosure can also provide an apparatus for detectingland pre-pits. The apparatus can include an extractor configured toextract a land pre-pit data stream from a reading signal based on a landpre-pit threshold, the reading signal corresponding to land pre-pits ofan optical medium, and a controller configured to compare the landpre-pit data stream with format information of the optical medium toobtain an error signal, and adjust the land pre-pit threshold based onthe error signal.

Furthermore, aspects of the disclosure can provide an optical drive. Theoptical drive can include an optical pickup unit configured to generatea reading signal corresponding to land pre-pits of an optical medium,and record data on the optical disc based on information extracted fromthe reading signal, an extractor configured to extract a land pre-pitdata stream from the reading signal based on a land pre-pit threshold,and a controller configured to compare the land pre-pit data stream withformat information of the optical medium to obtain an error signal, andadjust the land pre-pit threshold based on the error signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of this disclosure will be described indetail with reference to the following figures, wherein like numeralsreference like elements, and wherein:

FIGS. 1A and 1B show a block diagram of an exemplary medium device andan exemplary memory medium;

FIGS. 2A and 2B show a block diagram of an exemplary land pre-pit readchannel coupled to an exemplary optical pick-up unit (OPU) and anexemplary pick-up signal;

FIG. 3 shows a block diagram of an exemplary land pre-pit loopcontroller;

FIGS. 4A and 4B show an exemplary land pre-pit data format;

FIG. 5 shows a block diagram of an exemplary threshold adjuster;

FIGS. 6A-6C show waveforms of an exemplary land pre-pit read channel;and

FIG. 7 shows a flowchart outlining an exemplary process for detectingland pre-pits.

DETAILED DESCRIPTION OF EMBODIMENTS

FIGS. 1A and 1B show a block diagram of an exemplary medium device withan exemplary memory medium. The medium device 100 can include aprocessor 110, an optical drive 115, a RAM unit 130, and a non-volatilememory 140. These elements can be coupled together as shown in FIG. 1A.

The optical drive 115 can further include an optical pickup unit (OPU)120. The OPU 120 can receive signals corresponding to variousinformation, such as timing information, address information, discinformation, user data, and the like, in a memory medium, such as anoptical disc 190. For example, the OPU 120 may direct a laser beam to alocation of the optical disc 190. The laser beam can be reflected fromthe location of the optical disc 190. The reflected laser beam may havelight properties that can correspond to information embedded at thelocation of the optical disc 190. The light properties can be detectedby a light detector of the OPU 120. Further, the light detector of theOPU 120 may convert the light properties to electrical signals for othercomponents of the optical drive 115 to extract the various information,for example.

In addition, the OPU 120 can be configured to record user data on theoptical disc 190 according to the extracted information, such as timinginformation, address information, disc information, and the like. Forexample, the OPU 120 may direct a recording laser beam to a recordinglocation of the optical disc 190. The recording laser beam may have alaser power determined according to the extracted disc information, andmay have a turn-on time determined according to the extracted timinginformation. In addition, the recording location may be determined basedon the extracted address information, for example.

According to the disclosure, the optical drive 115 may include a landpre-pit (LPP) read channel 125 that can be configured to detect landpre-pits from an electrical signal converted by the light detector inorder to extract the embedded information. The land pre-pit read channel125 can include an adaptive land pre-pit threshold. The adaptive landpre-pit threshold can be used to determine a status, such as a binarystatus, of the electrical signal to detect the land pre-pits.

As shown in FIG. 1A, the optical disc 190 can generally include a spiralrecording track, for example in the form of a spiral groove adjacent toa spiral land. On the spiral recording track, user data can be stored ona recording layer by forming either data pits or data marks. The datapits or data marks can be preferred to have a substantially constantlinear length to improve the data storage capability of the optical disc190. To assist maintaining constant length of data marks or data pits,timing and address information can be encoded in the spiral groove andthe spiral land during disc manufacturing. In an example, the timinginformation can be encoded by wobbling the spiral groove and the spiralland. Further, address information and disk information can be encodedvia land pre-pits (LPP) for certain kinds of memory media, such asDVD-R, DVD-RAM and DVD-RW, and the like.

FIG. 1B shows an enlarged portion of an exemplary optical disc 190. Theoptical disc 190 can include alternatively arranged groove fields andland fields. The land fields can include land pre-pits. The landpre-pits can be produced by disc manufacturer. For example, during discmanufacturing, the disc manufacturer can deposit little pieces ofmirrors, such as aluminum, at specific locations of the land fields toform the land pre-pits.

The mirrors may have a higher reflectivity than areas without the landpre-pits. The higher reflectivity can be detected by the OPU 120. Forexample, the OPU 120 may direct a laser beam onto a location of theoptical disc 190. The laser beam can be reflected by the location. Thereflected laser beam may have light properties that can correspond to areflectivity of the location. When the laser beam is reflected by alocation with a deposited mirror, the reflected laser beam may have ahigher light intensity, for example. Further, the light properties maybe detected by a detector of the OPU 120. The detector may generateelectrical signals corresponding to the light properties. For example,the detector can generate a push-pull signal from the detected light.The push-pull signal may have an amplitude spike corresponding to alocation with a mirror.

Further, the push-pull signal can be compared to a land pre-pitthreshold to determine a status, such as a binary status, at a location.For example, when an amplitude of the electrical signal corresponding toa location is larger than the land pre-pit threshold, an amplitude spikecan be detected. Therefore, the location can be determined to have amirror. Thus, the location can be determined storing binary one, forexample.

Generally, a land pre-pit threshold can be determined by a calibrationprocess, and may be used globally to detect the land pre-pits. However,the globally used land pre-pit threshold can result in land pre-pitreading errors due to various reasons, such as manufacturing variations,gain variations and baseline variations of the electrical signal, noisesand interferences of adjacent groove fields, and the like. Further, theland pre-pit reading errors may result in poor recording qualities.

According to the disclosure, the medium device 100 can include anadaptive land pre-pit threshold. The adaptive land pre-pit threshold canbe adjusted based on format information of the land pre-pits. Theadaptive land pre-pit can be used to reduce land pre-pit reading errorsto improve recording quality.

The processor 110 of the medium device 100 can execute system andapplication codes. The non-volatile memory 140 can hold information evenwhen power is off. Therefore, the non-volatile memory 140 can be used tostore system and application codes, such as firmware. The RAM unit 130is readable and writable. Generally, the RAM unit 130 can have a fastaccess speed. It can be preferred that data and codes are stored in theRAM unit 130 during operation, such that the processor 110 can accessthe RAM unit 130 for the codes and data instead of the non-volatilememory 140.

It should be understood that the memory device 100 may include more thanone processor 110. Further, the non-volatile memory 140 may includevarious non-volatile memory devices, such as battery backup RAM, readonly memory (ROM), programmable ROM (PROM), flash PROM, electricalerasable PROM (EEPROM) magnetic storage, optical storage, and the like.Some non-volatile memory 140 can be updated, such as various types ofPROM. The RAM unit 130 may also include various RAM devices, such asDRAM, SRAM and the like.

For the ease and clarity of description, the embodiments are presentedwith a bus type architecture, however, it should be understood that anyother architectures can also be used to couple components inside memorydevice 100.

Additionally, the memory device 100 may include a user input module 160.The user input module 160 may enable the user to control operations ofthe memory device 100. The user input module 160 may include varioususer input devices, such as keyboard, mouse, touch screen, and the like.In addition, the user input module 160 may include interfaces that canenable external user input devices.

In an embodiment, the memory device 100 may include an audio/videomodule 150. The audio/video module 150 may include various audio andvideo devices, such as microphone, display screen, and the like. Inaddition, the audio/video module 150 may include interfaces that canenable external audio and video devices. The audio/video module 150 canbe utilized to play audio data/video data that can be stored in theoptical disc 190.

In another embodiment, the memory device 100 may include a networkmodule 170. Furthermore, the memory device 100 may include a wirelesscommunication module 180. The network module 170 and the wirelesscommunication module 180 may enable the memory device 100 to communicatethe data stored in the optical disc 190 to other devices.

FIGS. 2A and 2B show a block diagram of an exemplary land pre-pit readchannel receiving a push-pull signal and an exemplary waveform of apush-pull signal. FIG. 2A shows the block diagram of the exemplary landpre-pit read channel 225 coupled with an exemplary optical pickup unit220. Further, the land pre-pit read channel 225 can include a landpre-pit extractor 230 and a land pre-pit loop controller 240. Theseselements can be coupled as shown in FIG. 2A.

The optical pickup unit 220 may include a detector, such as a quadrantphoto detector 210 shown in FIG. 2A. The quadrant photo detector 210 maydetect a light beam 215, and generate various signals, including apush-pull signal (PPS), corresponding to the light beam 215. Thepush-pull signal can correspond to wobbled groove and land fields on amemory medium. Further, the push-pull signal can correspond to landpre-pits in the land fields for certain memory medium, such as DVD-R,DVD-RAM and DVD-RW.

The land pre-pit extractor 230 can receive the push-pull signal.Further, the land pre-pit extractor 230 can compare the push-pull signalwith an adaptive land pre-pit threshold to determine a land pre-pit datastream. In an embodiment, the land pre-pit extractor 230 may include ananalog comparator (not shown). The analog comparator may compare thepush-pull signal with the adaptive land pre-pit threshold to obtain apulse signal. Further, the pulse signal can be converted to the landpre-pit data stream based on a clock signal, such as a wobble clocksignal that can also be extracted from the push-pull signal.

The land pre-pit loop controller 240 can receive the extracted landpre-pit data stream and adjust the adaptive land pre-pit threshold basedon the extracted land pre-pit data stream. Further, the adjustedadaptive land pre-pit threshold can be used by the land pre-pitextractor 230 to extract a subsequent land pre-pit data stream from afollowing portion of the push-pull signal. In such a way, the landpre-pit loop controller 240 can couple the land pre-pit extractor 230 toform a land pre-pit feedback loop.

According to the disclosure, land pre-pits are formed by discmanufacture according to a pre-known format, such as an industrystandard. Therefore, the land pre-pit loop controller 240 may includethe pre-known format information about the land pre-pits. The landpre-pit loop controller 240 may extract detected format from the landpre-pit data stream. Further, the land pre-pit loop controller 240 cancompare the detected format with the pre-known format information, andadjust the adaptive land pre-pit threshold accordingly.

FIG. 2B shows an exemplary waveform of a push-pull signal. The push-pullsignal 250 can have a sinusoid shape as a result of wobbled groove andland fields. Further, the push-pull signal 250 may include spikes 260 asa result of land pre-pits at specific locations of land fields. Due tovarious variations, noises and interferences, amplitudes of the spikes260 may vary. Further, the amplitude variations of the spike 260 mayresult in detecting errors in the land pre-pit data stream.

FIG. 3 shows a block diagram of an exemplary land pre-pit loopcontroller according to disclosure. The land pre-pit loop controller 340may include a comparator 310, a threshold adjuster 320 and a landpre-pit format retainer 330 holding pre-known land pre-pit formatinformation. These elements can be coupled together as shown in FIG. 3.

The comparator 310 can receive a land pre-pit data stream and comparethe land pre-pit data stream with the pre-known land pre-pit formatinformation. Then, the comparator 310 can output an error signalcorresponding to difference between the land pre-pit data stream and thepre-known land pre-pit format information. In an embodiment, thecomparator 310 can be implemented as a software code module, which canbe executed by a processor (not shown) to compare the land pre-pit datastream with the pre-known land pre-pit format information. In anotherembodiment, the comparator 310 can be implemented as a hardware module,such as application specific integrated circuit (ASIC), to perform theabove functions.

The threshold adjuster 320 can receive the error signal and adjust theadaptive land pre-pit threshold based on the error signal. In anembodiment, the threshold adjuster 320 may adjust the adaptive landpre-pit threshold based on an average of the error signal. Additionally,the threshold adjuster 320 may include a programmable parameter, such asa programmable gain, which can be used to change properties of the landpre-pit feedback loop.

The land pre-pit format retainer 330 can include pre-known land pre-pitformat information. In an embodiment, the land pre-pit format retainer330 can be implemented in software codes that can be stored in a memorymedium, such as the random access memory (RAM) 130, the non-volatilememory 140, and the like, to hold the pre-known land pre-pit formatinformation. In another embodiment, the land pre-pit format retainer 330can include memory devices, such as registers, to hold the pre-knownland pre-pit format information.

FIGS. 4A and 4B show tables of exemplary land pre-pit formatinformation. FIG. 4A shows an exemplary pre-pit physical block formatinformation according to a standard. The pre-pit physical block 400 canbe encoded in the land fields, and can correspond to 16 sectors of datablocks, which are generally referred as ECC blocks, in the groovefields.

The pre-pit physical block 400 can include 16 sets pre-pits No. 0-No.15. Each set of pre-pits can include 26 SYNC frames, which are assignedeven (E) SYNC frames or odd (O) SYNC frames according to theirsequences. Each SYNC frame may include 8 wobble periods, and each wobbleperiod can be encoded a binary wobble bit depending on whether thewobble period includes a pre-pit. For example, a wobble period can beencoded with a binary wobble bit one if the wobble period includes apre-pit, otherwise the wobble period can be encoded with a binary wobblebit zero.

The wobble bits can be used to encode address information and discinformation according to certain format. In the example of FIG. 4A,every two SYNC frames can use the wobble bits to encode a code. The codecan be encoded at either the even SYNC frame or at the odd SYNC frame.Further, the code can be a SYNC code or a binary bit code according tocertain coding format.

FIG. 4B shows an exemplary coding format according to a standard. Thecoding format can use three wobble binary bits b₂-b₀ to encode the SYNCcode and the binary bit code in every two SYNC frames. In the example ofFIG. 4B, when the SYNC code is in even SYNC frame, the three wobblebinary bits b₂-b₀ are 111; when the SYNC code is in odd SYNC frame, thethree wobble binary bits b₂-b₀ are 110; when binary one is encoded, thethree wobble binary bits b₂-b₀ are 101; and when binary zero is encoded,the three wobble binary bits b₂-b_(o) are 100.

Accordingly, wobble bits information can be pre-known at certainlocations. For example, two SYNC frames that encode a SYNC code caneither be 1110000000000000 or 0000000011000000. In an embodiment, acomparator can generate an error signal based on the two SYNC framesthat encode a SYNC code. The comparator may store detected wobble bitsof two SYNC frames corresponding to a SYNC code in registers, which canbe referred as rawLPP[0:15]. Further, the comparator can generate theerror signal by comparing the detected wobble bits with the pre-knownformat information. For example, the comparator may assign −1 to theerror signal when 0 is detected at a location that should be 1 accordingto the pre-known format, and may assign 1 to error signal when 1 isdetected at a location that should be 0 according to the pre-knownformat.

In an embodiment, a comparator can be configured to generate an errorsignal according to following pseudo codes:

if rawLPP[0]|rawLPP[8]~=1 error signal <=−1 end if rawLPP[1] | rawLPP[9]| rawLPP[3:7] | rawLPP[11:15] ~=0 error signal <=+1 end

According to the disclosure, the error signal can be used by thethreshold adjuster 320 to adjust the adaptive pre-pit threshold toimprove the pre-pit detecting correctness. In an embodiment, thethreshold adjuster 320 can adjust the adaptive pre-pit threshold basedon an average of the error signal.

FIG. 5 shows a block diagram of an exemplary integrator circuit that canbe included in a threshold adjuster to generate a control signal basedon an error signal. The integrator 500 can include a multiplier 510, anaccumulator 520, and a register 530. These elements can be coupled asshown in FIG. 5.

The multiplier 510 can receive an error signal, and multiply the errorsignal with a programmable gain. The programmable gain can be used toadjust properties of the land pre-pit feedback loop.

The accumulator 520 and the register 530 can be coupled together tointegrate the multiplied error signal to generate an integrated errorsignal. Further, the integrated error signal can be used to adjust theadaptive land pre-pit threshold.

In an embodiment, a most significant bit of the integrated error signalcan be used to adjust a digital representation of the adaptive landpre-pit threshold. Further, the digital representation of the adaptiveland pre-pit can be converted to an analog voltage signal by a digitalto analog converter (DAC).

FIGS. 6A-6C show waveforms of an exemplary land pre-pit detector. FIG.6A shows waveforms of an exemplary push-pull signal read from an opticalmedium. The waveforms can include two portions, a wobble baselineportion 610 and a spike portion 620. The spike portion can correspond toamplitude spikes that area result from land pre-pits. However, as can beseen, the wobble based line portion 610 and the spike portion 620 maynot distinguishable by a single global threshold.

FIG. 6B and FIG. 6C show waveforms of exemplary adaptive land pre-pitthreshold according to two feedback loop settings, respectively. In anembodiment, the two feedback loop settings can correspond to differentvalues of a programmable gain of a feedback loop. For example, FIG. 6Bcan correspond to a feedback loop setting having a larger programmablegain, and FIG. 6C can correspond to a feedback loop setting having asmaller programmable gain. Accordingly, the adaptive land pre-pitthreshold may have different properties. For example, the adaptive landpre-pit threshold waveform in FIG. 6B can have a smaller bandwidth,while the adaptive land pre-pit threshold waveform in FIG. 6C can have alarger bandwidth.

FIG. 7 shows a flowchart outlining an exemplary process for detectingland pre-pit. The process starts at step S710 and proceeds to step S720.In step S720, a land pre-pit read channel, such as the land pre-pit readchannel 225, may receive a push-pull signal. Further, the land pre-pitread channel may extract a land pre-pit data stream based on an adaptivepre-pit threshold. In an embodiment, the adaptive pre-pit threshold canbe determined initially by a calibration process that calibratesparameters for a memory medium. The initial adaptive pre-pit thresholdcan be one that is good for a portion of the memory medium. In anotherembodiment, the initial adaptive pre-pit threshold can be a good nominalthreshold that can be pre-programmed in the memory medium. Then, theprocess proceeds to step S730.

In step S730, a controller, such as the land pre-pit loop controller240, may compare a portion of the land pre-pit data stream with apre-known format to obtain an error signal. In an embodiment, thecontroller may first detect a SYNC code. Once the SYNC code has beendetected and verified, the controller can compare the land pre-pitstream with the known format accordingly. For example, SYNC codes canappear every 26 SYNC frames according to a standard. Further, each SYNCcode can have a format of 1110000000000000 or a format of000000001100000. In an embodiment, the controller may generate −1 formissing a pre-pit at a location, and generate +1 for an unexpectedpre-pit at a location. Then the process proceeds to step S740.

In step S740, the controller may adjust the adaptive land pre-pitthreshold based on the error signal. In an example, the controller mayadjust the adaptive land pre-pit threshold based on an average of theerror signal. Then, the adjusted adaptive land pre-pit threshold can beused to extract land pre-pits from coming push-pull signal. The processthen proceeds to step S750 and terminates.

While the invention has been described in conjunction with the specificexemplary embodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart. Accordingly, exemplary embodiments of the invention as set forthherein are intended to be illustrative, not limiting. There are changesthat may be made without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A method for detecting land pre-pits, comprising:extracting a land pre-pit data stream from a signal responsive to landpre-pits on an optical medium based on a land pre-pit threshold;detecting a bit stream pattern from the land pre-pit data stream;comparing one or more bits in the land pre-pit data stream at locationsrelative to the bit stream pattern with pre-known bit information; andadjusting the land pre-pit threshold based on the comparison.
 2. Themethod according to claim 1, further comprising: determining an initialland pre-pit threshold during a calibration process.
 3. The methodaccording to claim 1, wherein adjusting the land pre-pit threshold basedon the comparison further comprises: generating an error signal based onthe comparison; and adjusting the land pre-pit threshold based on theerror signal.
 4. The method according to claim 3, wherein adjusting theland pre-pit threshold based on the error signal further comprises:adjusting the land pre-pit threshold based on an average of the errorsignal.
 5. The method according to claim 4, further comprising:averaging the error signal based on a programmable gain.
 6. The methodaccording to claim 5, wherein averaging the error signal based on theprogrammable gain, further comprising: multiplying the error signal withthe programmable gain; and accumulating the multiplied error signal. 7.The method according to claim 1, wherein adjusting the land pre-pitthreshold based on the comparison further comprising: adjusting adigital representation corresponding to the land pre-pit threshold; andconverting the digital representation to an analog voltage of the landpre-pit threshold.
 8. The method according to claim 1, wherein theoptical medium is at least one of DVD-R, DVD-RAM and DVD-RW.
 9. Anapparatus, comprising: an extractor configured to extract a land pre-pitdata stream from a signal responsive to land pre-pits on an opticalmedium based on a land pre-pit threshold; and a controller configured todetect a bit stream pattern from the land pre-pit data stream, compareone or more bits in the land pre-pit data stream at locations relativeto the bit stream pattern with pre-known bit information, adjust theland pre-pit threshold based on the comparison.
 10. The apparatusaccording to claim 9, wherein the controller is further configured todetermine an initial land pre-pit threshold during a calibrationprocess.
 11. The apparatus according to claim 9, wherein the controllerfurther comprises: a memory device configured to store the pre-known bitinformation.
 12. The apparatus according to claim 9, wherein thecontroller is further configured to generate an error signal based onthe comparison, and adjust the land pre-pit threshold based on the errorsignal.
 13. The apparatus according to claim 12, wherein the controlleris configured to adjust the land pre-pit threshold based on an averageof the error signal.
 14. The apparatus according to claim 12, whereinthe controller further comprises: a multiplier configured to multiplythe error signal with a programmable gain; and an accumulator configuredto accumulate the multiplied error signal.
 15. The apparatus accordingto claim 9, wherein the controller further comprises: a memory deviceconfigured to store a digital representation corresponding to the landpre-pit threshold; and a digital to analog converter (DAC) configured toconvert the digital representation to an analog voltage of the landpre-pit threshold.
 16. An optical drive, comprising: an optical pickupunit configured to generate a signal in response to a track on anoptical medium; an extractor configured to extract a land pre-pit datastream from the signal based on a land pre-pit threshold; and acontroller configured to detect a bit stream pattern from the landpre-pit data stream, comparing one or more bits in the land pre-pit datastream at locations relative to the bit stream pattern with pre-knownbit information, adjusting the land pre-pit threshold based on thecomparison.
 17. The optical drive according to claim 16, wherein thecontroller further comprises: a memory device configured to store thepre-known bit information.
 18. The optical drive according to claim 16,wherein the controller is further configured to generate an error signalbased on the comparison, and adjust the land pre-pit threshold based onthe error signal.
 19. The optical drive according to claim 18, whereinthe controller further comprises: a multiplier configured to multiplythe error signal with a programmable gain; and an accumulator configuredto accumulate the multiplied error signal, and the controller isconfigured to adjust the land pre-pit threshold based on the accumulatederror signal.
 20. The optical drive according to claim 16, wherein thecontroller further comprises: a memory device configured to store adigital representation corresponding to the land pre-pit threshold; anda digital to analog converter (DAC) configured to convert the digitalrepresentation to an analog voltage of the land pre-pit threshold.